The Minnesota Vikings kick off their offseason program in a week with a defense that has been changed dramatically since Mike Zimmer took over as the team's new head coach.

Zimmer has tried to reserve judgment on many of Minnesota's current roster until he has time to see each player on the field. The Vikings will hold a voluntary minicamp before May's NFL Draft. Zimmer's perception of the team's linebackers will be interesting.

Three weeks into free agency, Minnesota's plan at linebacker is anything but clear. Maybe even to Zimmer.

"You can ask me after we have the minicamp; I've worked with these guys a little bit, and you say, 'Hey, what do you think about the linebackers now?' and I'll give you a much better opinion than I have now," Zimmer said at February's NFL Scouting Combine. "I don't hardly know them at all."

Since Zimmer became the Vikings head coach in January, he's discussed the importance and differences of the defensive line in his system. Minnesota acted accordingly by not letting defensive end Everson Griffen reach free agency and then signing free agents Linval Joseph, Tom Johnson and Corey Wootton, along with also re-signing Fred Evans.

What's left is a linebacker corps that has many wondering what Zimmer's plan is for the second level of his defense.

Zimmer is withholding his opinion, at least publicly, on holdovers Chad Greenway, Audie Cole, Michael Mauti and Gerald Hodges. Greenway is the only returning full-time starter. Cole, Mauti and Hodges represent the youth at the position for Minnesota.

"We have some unproven guys there," Vikings general manager Rick Spielman said. "We're looking through some of this free-agent market and what's still available out there, but I also feel pretty strong about the draft and some of the depth that's in this draft class."

The draft has many intriguing options like Khalil Mack -- if he were to fall to Minnesota with the eighth pick -- C.J. Mosley, Ryan Shazier, Kyle Van Noy and Chris Borland among many strong options in the first few rounds.

Spielman offered an interesting perspective after the first week of free agency, though.

"I wish you could say you have 22 guys that you're going to line up with and say they're all proven starters," Spielman said. "That's not the way the NFL is. You have to plug in these young guys and you have to get them ready to play. We have an unbelievable coaching staff that I know will do a good job getting these guys ready to go.

"When you look at Audie Cole, he did a nice job when he came into Mike (middle linebacker). He can also play the strong side. Hodges can cross-train between the strong side and weak side. They're talking about doing some things with Chad Greenway, and Jasper Brinkley can play the 'Mike' and can play some strong side. I think all that stuff will kind of sort itself out once these guys get on the field and once we get through the draft and figure out what the best combination is for all these guys."

Greenway, the two-time Pro Bowl pick who played through a broken wrist last season, is the one constant. He's played in every game the past seven seasons and is one of the nickel linebackers when Minnesota switches to its three cornerback look.

So what changes could be in store for Greenway? Spielman wouldn't offer many specifics after hinting about an adjustment.

"I don't know," Spielman said about Greenway. "That's the coach's decision. I know he's played on the weak side and in our nickel package and stuff. They do a lot of things from a defensive side that's a little different than we've done in the past. Once these coaches figure out what the skill sets are and they get an opportunity to put their hands on players and figure out what their best skill set is, they figure out how to best utilize them on the field."